The hope for stem cell-based regenerative medicine is closer to reality than ever before. Recently, the Nobel Prize was awarded for the technology to generate induced pluripotent stem cells (iPSCs). As the name suggests, we can now induce non-embryonic cell sources to become stem cell-like, which could in turn be differentiated into specific cell types and even whole organs for regenerative medicine. Among many advantages this brings, this technology can help circumvent past ethical dilemmas surrounding the use of embryonic stem cells. In addition to iPSCs, human bodies also contain somatic (“adult”) stem cells that can be harnessed and be similarly coaxed to differentiate into regenerative cells. Commonly used somatic stem cells include the mesenchymal stem cells and neural stem cells. Regardless of the type, the new looming technical challenge is to generate an appreciate quantity of these therapeutic stem cells.
In addition to therapeutic stem cells, there is also a growing appreciation for the existence of malignant cancer stem cells (CSCs), which are hypothesized to uniquely possess properties of tumor initiation. Experimental evidence for their existence was first provided in leukemia stem cells. Subsequently, similar demonstration was provided for solid tumors including breast, brain, colon, and prostate cancers. Though the observation of tumor initiation in animal models is the current gold standard method of confirming the identity of CSCs, sphere formation and limiting dilution assays are also widely used surrogate in vitro methods of confirming CSC identity. This is based on the theory that a single CSC is sufficient to replicate into aggregates of cell spheres based on its self-renewal properties. Furthermore, it has been shown that cells isolated from resected tumor tissues retain their stemness better when grown as sphere aggregates in vitro, which is the same manner in which the aforementioned therapeutic stem cells are grown. Because CSCs are rare and difficult to acquire, there is a desire to expand them to advance oncology research, but this has been difficult and challenging.
For both therapeutic stem cells and malignant CSCs (collectively referred to henceforth as “stem cells”), the aggregates must be dissociated into single cells once grown to a critical sphere diameter. When spheres become too large, inadequate nutrient and oxygen supplies can cause premature necrotic cell death and negate the efforts to increase their number. Currently, this is a labor-intensive and time-consuming manual process that require physical trituration of the aggregates through a small orifice of pipette tips. In addition, it is unclear how such repeated shear stress affects the stem cells and how many of them survive the rather harsh processing.
Thus, there is a need in the art for a continuous and automated process for dissociating spheres of cells.